Hydrocarbon separation



y ,1970 R. D. BECKHAM ETAL 3,513,213

- HYDROCARBON SEPARATION Filed April 24, 1968 I NVENTOR. RODNEY D-BECKHAM BYHERBERT a. GEBHART, JR

EARLE c. MAKIN,JR.

Affornlj United States Patent 3,513,213 HYDROCARBON SEPARATION Rodney D.Beckham, Bridgeton, Herbert J. Gebhart, .lr.,

Ferguson, and Earle C. Makin, Jr., St. Louis, Mo., as-

signors to Monsanto Company, St. Louis, Mo., a corporation of DelawareFiled Apr. 24, 1968, Ser. No. 723,858 Int. Cl. C07c 7/10, /10

US. Cl. 260-674 10 Claims ABSTRACT OF THE DISCLOSURE A process forseparating vinyl aromatic hydrocarbons from alkyl aromatic hydrocarbonsemploying a substantially anhydrous silver salt. The vinyl aromatichydrocarbons are recovered from admixture with the silver salt bycontacting the mixture with an olefin and/ or diole| fin hydrocarbon.

BACKGROUND OF THE INVENTION The term vinyl aromatic hydrocarbons, asused herein, refers to aromatic hydrocarbons containing amonoethylenically unsaturated aliphatic substituent, e.g., styrene,a-methylstyrene, b-methylstyrene, vinyl toluene. Alkyl aromatichydrocarbons, as used herein, refers to those aromatic hydrocarbonshaving saturated aliphatic substituents, e.g., xylene, ethylbenzene andthe like.

One of the most difiicult separations problems existing in industrytoday is that of separating vinyl aromatic hydrocarbons from closeboiling alkyl aromatic hydrocarbons. In most instances, separation ofsuch hydrocarbons is difficult at best by distillation. However, torender the problem more difiicult, the unsaturated vinyl aromatichydrocarbons are usually easily polymerized and thus tend to polymerizeand foul the equipment used for separation by distillation. Probably themost exemplary and commonly encountered difficultly separable vinylaromatic hydrocarbons and alkyl aromatic hydrocarbons are styrene ando-xylene. These two compounds are very difficult to separate one fromanother and because of the entirely different uses of the two, eitherone of these is an undesirable contaminant in the other and, therefore,it is desired to have means for effectively separating the two.

In addition to distillation, it is known that such compounds as mercuricchloride, mercuric acetate, and the like, will complex With styrene.Such complex formation offers a means of separating styrene fromo-xylene. However, it is often quite difficult to recover the vinylaromatic hydrocarbons from the complex. Severe conditions usuallynecessary for recovering the complexed vinyl aromatic hydrocarbons fromthe complex often result in substantial polymerization and loss of thevinyl aromatic hydrocarbons.

An additional means of separating alkyl aromatic hydrocarbons from vinylaromatic hydrocarbons which has recently been proposed is a separationsprocess employing aqueous solutions of such silver salts as silverfiuoroice borate and silver fiuorosilicates. Such a separations processis disclosed and claimed in copending application Ser. No. 587,930,filed Oct. 16, 1966, now Pat. No.

' 3,427,362. While this means of separating alkyl aromatic hydrocarbonsfrom vinyl aromatic hydrocarbons represents a significant advancement insuch separation, it has been found desirable to find a means forincreasing the effectiveness of the usage of the silver salt ineffecting such separation.

It is now an object of the present invention to provide a new andimproved process for the separation of aromatic hydrocarbons. A furtherobject of the present invention is to provide a new and improved processfor the separation of vinyl aromatic hydrocarbons from alkyl aromatichydrocarbons. An additional object of the present invention is toprovide a new and improved process for the separation of vinyl aromatichydrocarbons from alkyl aromatic hydrocarbons wherein the vinyl aromatichydrocarbons can be substantially totally recovered. Yet another objectof the present invention is to provide a process for the separation ofvinyl aromatic hydrocarbons from alkyl aromatic hydrocarbons which as abenefit thereof provides a means whereby olefins and/ or conjugateddiolefins may be effectively removed from admixture with non-conjugateddiolefins and saturated hydrocarbons. Another object of the presentinvention is to provide a new and improved process for the separation ofstyrene from o-xylene. A particular object of the present invention isto provide a new and improved process for the separation of alkylaromatic hydrocarbons from vinyl aromatic hydrocarbons with a silversalt such as silver fluoroborate and silver fluorosilicate whereinsubstantially more effective use of the silver salts is obtained.Additional objects will become apparent from the following descriptionof the invention herein disclosed.

SUMMARY OF THE INVENTION The present invention which fulfills these andother objects, in one of its embodiments, is a process for theseparation of vinyl aromatic hydrocarbons from aromatic hydrocarbonmixtures containing vinyl aromatic hydrocarbons in admixture with alkylaromatic hydrocarbons. This process comprises contacting such aromatichydrocarbon mixtures With a substantially anhydrous silver salt selectedfrom the group consisting of silver fiuoroborate, silver fluorosilicateand mixtures thereof, separating an extract fraction containing saidsilver salt and aromatic hydrocarbons in solution therewith, and arafflnate fraction containing aromatic hydrocarbons not in solution withsaid silver salt, and recovering from said extract fraction an aromatichydrocarbon fraction sub; stantially richer in vinyl aromatichydrocarbons than the initial aromatic hydrocarbon mixture. Tofacilitate the use of the substantially anhydrous silver salts used inthe process of the present invention, the silver salt most often is usedin solution with an organic solubilizing agent for such silver salt.

As a useful mode of operating the process of the present invention, thearomatic hydrocarbon mixture containing vinyl aromatic hydrocarbons andalkyl aromatic hydrocarbons is contacted with the substantiallyanhydrous silver salt and the resulting mixture of silver salt andaromatic hydrocarbons then contacted with a saturated aliphatichydrocarbon of 3 to 15 carbon atoms. When the saturated aliphatichydrocarbons are contacted with the mixture of aromatic hydrocarbons andsilver salt in accordance with the process defined herein, extract andraffinate phases are more readily formed and the efficiency of theseparation of alkyl aromatic hydrocarbons from vinyl aromatichydrocarbons is thereby improved.

The recovery of the vinyl aromatic hydrocarbons from the extract phasemay be accomplished by any available means. The vinyl aromatichydrocarbons may be distilled from the extract phase. However, it isgenerally desired to carry out such a distillation under reducedpressure to avoid high temperatures which would likely causepolymerization of the vinyl aromatic hydrocarbons as well asdecomposition of the silver salt. When distillation is used as the meansof recovering the vinyl aromatic hydrocarbons from the extract phase,reduced pressures within the range of 75 to 300 mm. Hg are preferred.

A particularly useful method of recovering the vinyl aromatichydrocarbons from the silver salt containing extract phase comprisescontacting such extract phase with an unsaturated aliphatic hydrocarbonselected from the group consisting of olefins, diolefins and mixturesthereof. It has been found that the olefins and/ or diolefins when inmolar excess will displace vinyl aromatic hydrocarbons from the extractphase and are in turn preferentially absorbed and retained therein. Theolefins and/ or diolefins may be removed from the new extract phase bydistillation under significantly less stringent conditions oftemperature and pressure than those required for the removal of vinylaromatic hydrocarbons. However, quite surprisingly, the olefins and/ordiolefins, as the case may be, may in turn be displaced from the extractphase by contact with at least an equimolar quantity of vinyl aromatichydrocarbons. In view of the ability of the olefins and/or diolefins todisplace the vinyl aromatic hydrocarbons and in turn the vinyl aromatichydrocarbons to displace the olefins and/or diolefins from the silversalt containing phase, the present invention in a particularly usefulembodiment provides a dual process whereby vinyl aromatic hydrocarbonsmay be separated from alkyl aromatic hydrocarbons and olefins and/ordiolefins such as isoprene, may be separated from saturatedhydrocarbons, etc., using the same solvent solution and, if desired, thesame or substantially the same equipment. In addition, conjugateddiolefins may be separated from non-conjugated diolefins in this step.Such a dual process comprises (1) contacting a mixture of aromatichydrocarbons containing vinyl aromatic hydrocarbons and alkyl aromatichydrocarbons with a substantially anhydrous silver salt selected fromthe group consisting of silver fluoroborate, silver fiuorosilicate andmixtures thereof, (2) separating first raffinate fraction and a firstextract fraction, (3) contacting said first extract fraction with amixture of hydrocarbons containing olefins and/or diolefins in admixturewith saturated hydrocarbons and/or other hydrocarbons or a mixture ofconjugated and non-conjugated diolefins, the quantity of said mixture ofhydrocarbons being such that the olefins and/ or diolefins are in molarexcess to said vinyl aromatic hydrocarbons contained in said firstextract fraction, thereby displacing aromatic hydrocarbons from saidfirst extract fraction and forming a second extract fraction comprisingsaid silver salt and unsaturated aliphatic hydrocarbons and a secondraffinate fraction comprising the hydrocarbons not absorbed in saidsecond extract fraction and the aromatic hydrocarbons displaced fromsaid first extract fraction, (4) separating said second rafiinatefraction and said second extract fraction and (5) recycling at least apart of said second extract fraction to step (1) above as a substitutefor at least a part of said substantially anhydrous silver salt andthereafter continuously repeating the above steps.

DESCRIPTION OF THE DRAWING The accompanying drawing is a diagrammaticrepresentation of a particularly useful and practical method of carryingout the dual process of the present invention.

4 DESCRIPTION OF THE PREFERRED EMBODIMENTS To further describe the abovedisclosed dual process of the present invention which provides for theseparation of vinyl aromatic hydrocarbons from alkyl aromatichydrocarbons and also for the separation of olefins and/ or conjugateddiolefins from non-conjugated diolefins and other hydrocarbons,reference is made to the drawing. With reference to the drawing, anaromatic hydrocarbon mixture containing vinyl aromatic hydrocarbons andalkyl aromatic hydrocarbons is introduced into a liquid-liquidextraction column 10 by means of feed entry line 11. Concurrently withthe introduction of the aromatic mixture by line 11, a solvent comprisedof a substantially anhydrous silver salt which is either silverfluoroborate, silver fiuorosilicate, or a combination thereof, and anorganic solubilizing compound capable of dissolving the silver salt, isintroduced into column 10 by means of solvent entry line 12. Lines 11and 12 are shown intersecting column 10 at a point near but below thetop of column 10 and at substantially the same distance from the top ofcolumn 10. In this embodiment, lines 11 and 12 should be so arrangedthat the compositions introduced thereby will intimately co-mingle onewith another, almost immediately upon entering column 10. Anyarrangement which will accomplish this end may be substituted for thatshown in the drawing. To facilitate such co-mingling, it is desirable toprovide mechanical means with the column to aid in such co-mingling.Examples of such means are trays, rotating discs, packings, etc.Concurrently with the introduction of the aromatic hydrocarbons via line11 and solvent via line 12, a saturated aliphatic hydrocarbon of 3 to 15carbon atoms is introduced into column 10 by means of line 13. Thisaliphatic hydrocarbon flows upwardly through column 10 countercurrentlycontacting descending solvent and aromatic hydrocarbon feed. A raffinatephase is continuously taken overhead from column 10 by line 14 throughwhich the raflinate phase is passed to distillation or other recoverymeans (not shown) whereby the components of the rafiinate are separated.The components of the raflinate in continuous operation include thealiphatic hydrocarbon, the aromatic hydrocarbons not absorbed by thesolvent and any unsaturated aliphatic hydrocarbons which were containedin the solvent at the time of its entering column 10 by line 12.

An extract phase is continuously taken from column 10 by line 15. Thisextract phase, referred to as the first extract phase, contains thesilver salt and aromatic hydrocarbons of the feed mixture which go intosolution therewith.

The first extract phase is introduced into a second extraction column 16in which the first extract phase passes downwardly countercurrentlycontacting upfiowing unsaturated aliphatic hydrocarbons comprised ofolefins and/or diolefins and/or other hydrocarbons which enter column 16by unsaturated hydrocarbon feed line 17, and upfiowing saturatedaliphatic hydrocarbons of 3 to 15 carbon atoms which enter column 16 byline 18. A second raffinate phase is continuously taken overhead fromcolumn 16 by line 19. This second rafiinate phase is carried by line 19to distillation or other recovery means (not shown) whereby thecomponents of the second raffinate phase are separated. The componentsof the second rafiinate phase comprise the saturated aliphatichydrocarbon, the non-absorbed portion of the unsaturated hydrocarbons,and the aromatic hydrocarbons which were contained in the first extractphase at the time it entered column 16 by line 15.

By means of line 20, an extract phase, referred to as the second extractphase, is removed from column 16 and at least a portion thereof isreturned through line 20 to line 12 for re-use in column 10. This secondextract phase contains the silver salt and unsaturated aliphatichydrocarbons absorbed therein.

The solubilizing organic compound used to obtain the substantiallyanhydrous silver salt solution is found in the first rafiinate phase orin the first extract phase or partially in both phases, depending uponthe particular solubilizing organic compound used, the particularcomponents of the feed material, the ratio of the components of the feedmaterial to the solubilizing organic compound and other factors. If aportion of the solubilizing agent is present in the first extract phase,then the solubilizing agent also may be found in the second rafiinatephase, the second extract phase or partially in both. As will be furtherdiscussed herein below, consideration should be given to the ease withwhich the materials of the feeds can be separated from the solubilizingorganic compounds in selecting such compounds for dissolving theanhydrous silver salt.

Those skilled in the art will readily appreciate that many modificationsof the above-described dual process of the present invention and thearrangement of equipment therefor, may be made. However, so long as suchmodifications depend upon the principles and concepts above discussed,such modifications may be practiced without departing from the spiritand scope of the present invention.

To further describe and to specifically illustrate the presentinvention, the following examples are presented. These examples are notto be construed as in any manner limiting the present invention.

Example I Eight grams of a mixture consisting of 4.0 grams of styreneand 4.0 grams of a substantially pure o-xylene, were agitated withapproximately ml. of a silver fluoroborate solution at a temperature of25 C. The silver fiuoroborate solution consisted of 2.04 grams of silverfluoroborate dissolved in 8.0 grams of toluene. The agitation wasstopped and a raffinate and extract phase allowed to form. The extractand raffinate phases were then separated. This extract phase was thenagitated with 12 grams of petroleum ether and a second extract andrafiinate phase allowed to form. These phases were separated and thesecond raffinate phase combined with the first raffinate phase to form atotal raffinate phase. The second extract phase and the total raflinatephase were each analyzed. The following table represents the weightpercent toluene in each phase and the composition on a toluene-freebasis of the aromatic hydrocarbon feed, the total rafiinate, and theextract.

TABLE Feed Rafiinate Styrene 50. 0 41. 55 O-xylene 50. 0 58. 45 Toluene54. 15

Component (wt. percent) The amount of styrene in the extract representsa 116.3% utilization of all of the available silver fluoroborate.

Example 11 Four grams of a mixture containing 2 grams of styrene and 2grams of substantially pure ethylbenzene, were agitated withapproximately 4 ml. of a silver fiuoroborate solution at C. The silverfiuoroborate solution consisted of 1.0 gram of silver fluoroboratedissolved in 5.0

grams sulfolane. On stopping agitation, no phasing oc- TABLE FeedRatfinate Extract Component (wt. percent) Styrene Ethylbenzene r ExtractThe amount of styrene in the extract represents a 102.8% utilization ofall of the available silver fluoroborate.

Example III The extract (6.6 grams) of Example II was intimatelycontacted with 3 grams of n-pentene-l to form an extract and a raffinatephase. These phases were separated and the extract phase contacted withan additional 3 grams of n-pentene-l to form a second extract andrafiinate phase. This second extract and raffinate phase was separatedand the first and second rafiinate phases combined to form a totalraffinate phase. These phases were analyzed for hydrocarbon composition.The following table presents the hydrocarbon composition of the extractfrom Example II and the extract and total ratfinate formed in thisExample III.

Sixteen grams of a mixture containing 8.0 grams of styrene and 8.0 gramsof substantially pure o-xylene, were agitated with 8 ml. of a silverfiuoroborate solution at 25 C. The silver fluoroborate solutionconsisted of 4.0 grams of silver fluoroborate dissolved in 4.0 grams ofa mixture of 3.2 grams of sulfolane and 0.8 gram of Water. Agitation wasstopped and a raffinate and extract phase allowed to form. These phaseswere separated and the extract phase agitated with approximately 30 mls.of petroleum ether to form a second extract and raffinate phase. Thesecond raffinate phase was combined with the first raffinate phase toform. a total rafiinate phase which, along with the second extractphase, was analyzed. The following table presents the weight percento-xylene and styrene in the feed and the extract and rafiinate phases.

The amount of styrene in the extract represents a 47.0% utilization ofall of the available silver fluoroborate.

Example V Eight grams of a mixture consisting of 4.0 grams of styreneand 4.0 grams of substantially pure o-xylene, were agitated withapproximately 10 mls. of a silver fluoroborate solution at 25 C. Thesilver fiuoroborate solution consisted of 2.0 grams of silverfiuoroborate dissolved in a mixture of 6.4 grams of sulfolane and 1.6grams of water. Agitation was stopped and a raffinate and extract phaseallowed to form. The extract and raffinate phases were separated and theextract phase agitated with petroleum ether to form second extract andraffinate phases. The second raffinate phase was combined with the firstraffinate phase to form a total raffinate phase and this total ratfinatephase and second extract phase were analyzed. The following tablepresents the weight percent of styrene and o-xylene in the extract andraifinate phases.

The amount of styrene in the extract represents a 14.0% utilization ofall of the available silver fluoroborate.

A comparison of Examples I, II, IV and V with respect to the efficiencyof utilization of the silver fluoroborate clearly illustrates theimportance of using a substantially anhydrous silver salt in thepractice of the present invention. While the use of silver salt solventsolutions containing water does bring about the desired separation, thequantity of silver salt required to separate and recover a givenquantity of styrene becomes much greater as the water content increases.Comparison of Examples IV and V also indicates the effect ofconcentration of the silver salt. The higher the concentration, the moreeffectively the silver salt is utilized.

The silver salts used in the process of the present invention includesilver tetrafluoroborate, more commonly known as silver fluoroborate,and silver tetrafluorosilicate, more commonly known as silverfluorosilicate. These silver salts may be used alone or in combination.The preferred silver salt is the silver fluoroborate.

By substantially anhydrous as used herein, is meant a silver salt inadmixture With or containing less than 15% by weight of water inadmixture with the silver salt. Most often, the substantially anhydroussilver salt contains less than 10% Water, preferably, less than byweight.

In utilizing the silver salt in solution with an organic solubilizingagent, the silver salt solution will contain the silver salt in aconcentration of to 90% by weight of the solution. Preferred, however,are concentrations of to 60% by weight.

In carrying out the process of the present invention, most often about0.2 to 20 parts by weight of silver salt per part by weight of vinylaromatic hydrocarbons the aromatic hydrocarbon mixture to be separatedare employed. Preferably, however, the amount of silver salt used isWithin the range of 0.5 to 10 parts by weight per part by weight ofvinyl aromatic hydrocarbons.

When olefins and/or diolefins are employed to displace the vinylaromatic hydrocarbons from the silver salt containing extract or theprocess of the present invention is operated as a dual process, as abovedescribed, it is generally desirable that the amount of olefins and/ordiolefins contacted with the vinyl aromatic hydrocarbon silver saltcontaining extract be in weight ratio to the silver salt within therange of from 5:1 to 70:1, preferably within the range of from 10:1 to:1. Within these ranges, however, it is necessary that the amount ofolefin and/or diolefin employed always be greater on a molar basis, thanthe amount of vinyl aromatic hydrocarbons contained in the silver saltcontaining extract.

The organic solubilizing agents useful in the practice of the presentinvention include aromatic hydrocarbons, non-aromatic unsaturatedhydrocarbons and oxygenated compounds. The aromatic hydrocarbons usefulas solubilizing agents may contain a single aromatic ring or may containtwo or more aromatic rings, either condensed or noncondensed. Inaddition, the aromatic hydrocarbons may have substituents to the ring ormay be condensed with one or more other ring structures which areparaffinic or olefinic in nature. Non-limiting examples of aromatichydrocarbons suitable as solubilizing agents in the practice of thepresent invention are benzene, toluene, the xylenes, various otherpolymethylbenzenes, such as mesitylene, isodurene, tri-, tetra-, penta-,and hexamethylbenzenes; ethylbenzene and the various poly ethylbenzenes,isopropylbenzene, propylbenzene and the various polyisopropyl andpolypropyl benzenes, the various butyl and pentyl benzenes and the like;the substituted benzenes containing two or more different substituentssuch as ethyltoluene isopropyltoluene and ethylxylenes; the variousmethylnaphthalenes, and polymethylnaphthalenes, ethylnaphthalene and thevarious polyethylnaphthalenes, the naphthalenes containing propyl,isopropyl, butyl, and pentyl substituents; the substituted naphthalenescontaining two or more different substituents such as methylethylnaphthalene, methylpropyl naphthalene, and the like; the various indanessuch as methylindane, ethylindanes, isopropylindanes, and the like; thedihydronaphthalenes such as methyl, ethyl, propyl, and butyl substituteddihydronaphthalenes; the tetrahydronaphthalenes such as methyl, ethyl,propyl, and pentyl substituted tetrahydronaphthalenes and the like; thevinyl aromatic hydrocarbons such as styrene, alpha-methyl styrene, vinyltoluene, and the like. In the preferred practice of the presentinvention utilizing aromatic hydrocarbons as the solubilizing agent forthe silver salt, the aromatic hydrocarbons are the mononuclear aromaticscontaining 6 to 12 carbon atoms. The substituents to such aromatichydrocarbons may be straight-chain, branched chain or cyclic and may besaturated or unsaturated.

The non-aromatic unsaturated hydrocarbons useful in practicing thepresent invention include olefins, both acyclic and alicyclic, anddiolefins. Among the acyclic olefins useful as solubilizing agents aresuch compounds as hexene-l, hexene-Z, methylhexenes, dimethylhexenes,heptenes, methylheptenes, dimethylheptenes, ethylheptenes, nonenes,methylnonenes, dimethylnonenes, ethylnonenes, methylethylnonenes,diethylnonenes, propylnonenes, decenes, ethyldecenes, dimethyldecenes,methyldecenes, diethyldecenes, methylethyldecenes, propyldecenes,dipropyldecenes, methylpropyldecenes, and the like on up to andincluding such acyclic compounds having 15 carbon atoms. The alicyclicolefins useful in the practice of the present invention include suchcompounds as cyclohexene, methylcyclohexene, dimethylcyclohexenes,ethylcyclohexenes, cycloheptene, methylcycloheptene,dimethylcycloheptenes, ethylcycloheptenes, diethylcycloheptenes,methylethylcycloheptenes, cyclooctene, methylcyclooctene,dimethylcyclooctenes, trimethylcyclooctenes, ethylcyclooctene, and thelike up to and including alicyclic olefins having up to 10 carbon atomsin one or more substituents to the ring. In addition, such alicyclicolefins as those containing two or more rings in which only one of therings contains olefinic unsaturation may be used as a solubilizing agentin the practice of the present invention. The diolefinic hydrocarbonsuseful as solubilizing agents include both the cyclic and noncyclicdiolefinic hydrocarbons and include such compounds as pentadienes,hexadienes, heptadienes, octadienes, on up to and including thosecontaining as high as 15 carbon atoms and higher. These diolefinsinclude both those having no substituents as well as those having one ormore alkyl substituents. In the preferred practice of the presentinvention utilizing non-aromatic unsaturated hydrocarbons as thesolubilizing agent for the silver salt, olefin hydrocarbons of 6 to 15carbon atoms are employed. These may be either cyclic or non-cyclic.

The oxygenated compounds which may be used as solubilizing agents in thepractice of the present invention include ethers, ketones, alcohols,glycols, sulfones and the like. The ethers useful include acylic ethers,alicyclic ethers, aryl ethers and alkyl aryl ethers. The acyclic ethersinclude such compounds as diethyl ether, di-npropyl ether, di-n-butylether, di-isopropyl ether, di-isobutyl ether, di-tert-butyl ether,di-n-octyl ether and the like. Among the alicyclic ethers are suchcompounds as tetrahydrofuran, 1,4-dioxane, 1,3-dioxane,alkyl-substituted ethylene oxides, and the like. Useful aryl and alkylaryl ethers include such compounds as diphenyl ether, ditolyl ether,methyl phenyl ether, methyl tolyl ether and the like.

Among the ketones useful in the practice of the present invention arethe alkyl ketones such as dimethyl, diethyl, di-n-propyl, di-n-butyl,di-n-pentyl, di-n-hexyl and corresponding di-iso-alkyl or mixediso-normal alkyl ketones. Particularly useful among the ketones arethose in which the alkyl radicals contain 1 to 6 carbon atoms. Amongthis useful group are such compoundsas dimethyl, diethyl, di-nandisopropyl, di-n-, iso-, and sec-butyl, di-n-, iso-, and sec-pentylketone, di-n-, iso-, hexyl ketone, etc.

The alcohols useful as solubilizing agents in carrying out the presentinvention include the acyclic, alicyclic, and the aryl alcohols. Severalnonlimiting examples of such alcohols are methyl alcohol, ethyl alcohol,cyclohexanol, benzyl alcohol and the like. When using alcohols assolubilizing agents, it is usually somewhat preferred to use thosehaving no geater than 8 carbon atoms with the acyclic alcohols beingsomewhat preferred over the alicyclic and aryl alcohols. Particularlyuseful are nonaromatic alcohols having 1 to 6 carbon atoms and includingsuch alcohols as methyl alcohol, ethyl alcohol, propyl alcohol,isopropyl alcohol and the isomeric butyl alcohols.

The glycols useful in the practice of the present invention are mostoften those having 2 to 6 carbon atoms. Several non-limiting examples ofsuch alcohols are ethylene glycol, propylene glycol, diethylene glycol,triethylene glycol, and the like. Particularly useful, are such glycolsas ethylene glycol and propylene glycol and other such glycolscontaining 2 to 4 carbon atoms.

Another useful group of oxygenated compounds useful as solubilizingagents in the practice of the present invention are the sulfones. Withinthis group are both the alkyl and aryl sulfones. Particularly useful arethe aryl sulfones such as tetramethylene sulfone (sulfolane) and itsalkyl substituted derivatives wherein the alkyl group or groups has 1 to6 carbon atoms.

The aromatic hydrocarbon mixture containing vinyl aromatic hydrocarbonsand alkyl aromatic hydrocarbons which is to be separated in accordancewith the present invention generally is contacted with the silver saltat a temperature within the range of -30- to 70 C., preferably -20 to 50C. Pressure does not appear to be critical in the separation andrecovery of the vinyl aromatic hydrocarbons by means of thesubstantially anhydrous silver salt. Therefore, the pressure at whichthe process of the present invention is operated is generally based uponpracticality.

The period of contact of the aromatic hydrocarbon mixture to beseparated with the silver salt may be very short. As a practical matter,the period of contact will vary considerably depending upon theelliciency of the means employed for contacting the aromatichydrocarbons with the silver salt. The determination of the optimumperiods of contact are well within the ability of those skilled in theart and thus require no discussion herein.

When the process of the present invention is operated as a dual processand olefins and/ or diolefins are used to displace and recover the vinylaromatic hydrocarbons from the silver salt, the same conditions as totemperatures, pressures and contact time may be used as are used forcontact of the aromatic hydrocarbons with the silver salt.

It has been found particularly useful in carrying out the process of thepresent invention to use saturated aliphatic hydrocarbons of 3 to carbonatoms per molecule to aid in separating aromatic hydrocarbons which arenot absorbed by the silver salt from such silver salt. As noted above,the use of the saturated aliphatic hydrocarbons of 3 to 15 carbon atomsgreatly facilitates the formation of an extract and rafiinate phase andthereby considerably simplifies the present separations process.Non-limiting examples of such hydrocarbons are propane, n-butane,npentane, n-hexane, n-heptane, n-octane, n-nonane, ndecane, n-undecane,n-dodecane, n-tridecane, isobutane, isopentane, isoheptanes, isodecanes,isododecanes, isotridecane, cyclopentane, cyclohexane,methylcyclohexane, cycloheptane, and the like. Most often, the saturatedaliphatic hydrocarbons are paraffinic hydrocarbons and may bestraight-chain or branched-chain. Petroleum ether is a very practicaland useful fraction for use in the present process. The most usefulsaturated aliphatic hydrocarbons are the parafiinic hydrocarbons of 4 to7 carbon atoms per molecule.

The amount of saturated aliphatic hydrocarbons of 3 to 15 carbon atomsused in the process of the present invention may vary considerably. Theactual amount of such aliphatic hydrocarbons used will depend to a largeextent on the amount of alkyl aromatic hydrocarbons in the aromatichydrocarbon mixture and the degree of separation desired, etc. Usually,however, about 0.5 to 10 volumes of saturated aliphatic hydrocarbon willbe used per volume of alkyl aromatic hydrocarbon in the aromatichydrocarbon feed mixture to be separated. Preferably, however, about 1to 3 volumes of the saturated aliphatic hydrocarbon will be used pervolume of alkyl aromatic hydrocarbons in the feed mixture.

In employing the saturated aliphatic hydrocarbons of 3 to 15 carbonatoms to remove unabsorbed alkyl aromatic hydrocarbons from the silversalt, these aliphatic hydrocarbons may be contacted with the mixture ofsilver salt and aromatic hydrocarbons absorbed therein after the initialcontact and agitation of the aromatic hydrocarbon feed with the silversalt has ceased or the saturated aliphatic hydrocarbon may be broughtinto contact with the silver salt simultaneously with the aromatichydrocarbon feed which is to be separated. Further, the saturatedaliphatic hydrocarbon may be introduced concurrently with the aromatichydrocarbon mixture to be separated and into countercurernt contact withthe silver. Instead, however, the saturated aliphatic hydrocarbons maybe contacted countercurrently with the aromatic hydrocarbon mixture tobe separated and the silver salt.

The aromatic hydrocarbon mixtures which may be separated in accordancewith the present invention are those containing vinyl aromatichydrocarbons and alkyl aromatic hydrocarbons. While the hydrocarbons, itis most practical for the separation of aromatic hydrocarbon mixturescontaining vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbonswithin the C to C range. The present invention is particularly usefuland practical for the separation of styrene from close boiling o-xyleneand for the separation of a-methylstyrene and/ or vinyl toluene fromclose boiling alkyl aromatic hydrocarbons.

The olefins and/or diolefins useful in displacing absorbed vinylaromatic hydrocarbons from the silver salt are preferably thosecontaining 2 to 8 carbon atoms per molecule though those having highernumbers of carbon atoms may be used. These olefins and/or diolefins maybe in relatively pure state or may be in admixture with otherhydrocarbons such as paraffins, naphthenes or even alkyl aromatichydrocarbons. Additionally, the present invention provides a means forseparating conjugated diolefins from non-conjugated diolefins since theconjungated diolefins are preferentially absorbed in the silver saltsolution. Therefore, mixtures of these diolefins may be employed. Inchoosing the olefin or diolefin or a mixture of such unsaturatedcompounds with one another or with saturated compounds to be used fordisplacing the vinyl aromatic hydrocarbons, care should be taken thatthese compounds are not so similar in boiling point or so capable offorming an azeotope with the vinyl aromatic hydrocarbons as to presentnew separation problems in recovering the vinyl aromatics. While theolefins and/or diolefins may be cyclic, straight-chain or branched-chainin structure, it is preferable that they be straight or branched-chain.When the present invention is operated with a C to C aromatichydrocarbon feed mixture containing vinyl aromatic hydrocarbons,isoprene or other conjugated diolefins of 5 to 7 carbon atoms areparticularly useful.

What is claimed is:

1. A process for the separation of vinyl aromatic hydrocarbons fromaromatic hydrocarbon mixtures containing vinyl aromatic hydrocarbons, inadmixture with alkyl aromatic hydrocarbons, which comprises contactingsaid aromatic hydrocarbon mixture with a substantially anhydrous silverfluoroborate, separating an extract fraction containing said silverfluoroborate and the aromatic hydrocarbons in solution therewith, and araffinate fraction containing aromatic hydrocarbons not in solution 11with said silver fluoroborate, and recovering from said extract fractionan aromatic hydrocarbon fraction substantially richer in vinyl aromatichydrocarbons than the initial aromatic hydrocarbon mixture.

2. The process of claim 1 wherein the substantially anhydrous silverfluoroborate is in solution with an organic solubilizing agent, theamount of silver fluoroborate in said solution being within the range ofto 90% by weight of said solution.

3. The process of claim 1 wherein the amount of silver fiuoroboratecontacted with said aromatic hydrocarbon mixture is such as to cause aratio by weight of silver fiuoroborate to vinyl aromatic hydrocarbons insaid aromatic hydrocarbon mixture within the range of about 0.2:1 to 20:1.

4. The process of claim 1 wherein the aromatic hydrocarbon mixture isone containing vinyl aromatic hydrocarbons and alkyl aromatichydrocarbons within the C to C range.

5. The process of claim 1 wherein the aromatic hydrocarbon mixture iscontacted with the silver fluoroborate at a temperature within the rangeof 30 to 70 C.

6. The process of claim 1 wherein the mixture resulting from thecontacting of the aromatic hydrocarbon mixture with the silverfluoroborate is contacted with a saturated aliphatic hydrocarbon of 3 tocarbon atoms.

7. The process of claim 6 wherein about 0.5 to 10 volumes of saidsaturated aliphatic hydrocarbon is used per volume of alkyl aromatichydrocarbon in the aromatic hydrocarbon mixture which is contacted withthe silver fluoroborate.

8. The process of claim 6 wherein the saturated aliphatic hydrocarbon isa non-cyclic parafiinic hydrocarbon of 4 to 7 carbon atoms per molecule.

9. The process of claim 1 wherein said aromatic hydrocarbon fractionsubstantially richer in vinyl aromatic hydrocarbons than the initialaromatic hydrocarbon mixture is recovered from said extract fraction bycontacting said extract fraction with an amount of an unsaturatedaliphatic hydrocarbon selected from the group consisting of olefins andconjugated diolefins such that said unsaturated aliphatic hydrocarbon isin molar excess to the vinyl aromatic hydrocarbons contained within saidextract fraction.

10. A process for the separation of vinyl aromatic hydrocarbons fromalkyl aromatic hydrocarbons and unsaturated aliphatic hydrocarbonsselected from the group consisting of olefins and conjugated diolefinsfrom mixtures of such unsaturated hydrocarbons with other hydrocarbonswhich comprises (1) contacting a mixture of aromatic hydrocarbonscontaining vinyl aromatic hydrocarbons and alkyl aromatic hydrocarbonswith substantially anhydrous silver fluoroborate, (2) separating a firstraffinate fraction containing the nonabsorbed aromatic hydrocarbons anda first extract fraction containing the silver fluoroborate and thearomatic hydrocarbons in solution therewith, (3) contacting saidfirst'extract fraction with a mixture of hydrocarbons containingunsaturated aliphatic hydrocarbons selected from the group consisting ofolefins and conjugated diolefins, the quantity of said mixture ofhydrocarbons being such that said unsaturated aliphatic hydrocarbonscontained in said first extract fraction, thereby displacing thearomatic hydrocarbons absorbed in said first extract fraction andforming a second extract fraction comprising said silver fluoroborateand said unsaturated aliphatic hydrocarbons in solution therewith and asecond ratfinate fraction comprising the hydrocarbons not in solutionwith said silver fluoroborate and the aromatic hydrocarbons displacedfrom said first extract fraction, (4) separating said second r'aflinatefraction and said second extract fraction,and (5) recycling at least apart of said second extract fraction to step (1) above as a substitutefor at least a part of said silver fluoroborate and thereaftercontinuously repeating the above steps.

References Cited UNITED STATES PATENTS 2,391,404 12/1945 Friedman et a1.260--669 XR 2,458,067 1/ 1949 Friedman et a1. 260-669 XR 3,427,362 2/1969 Beckham et a1. 260-674 DELBERT E. GANTZ, Primary Examiner C. R.DAVIS, Assistant Examiner US. Cl. X.R. 260-669

